1. Field of the Invention
The present invention relates to systems for transferring data between computer systems, and more particularly to systems which use communications across a routed network to establish communication pathways across a connection-oriented network.
2. Related Art
Advances in computer networking technology have led to the development of applications such as video conferencing, which require sustained high bandwidth transmissions across computer networks. Providing such high bandwidth transmissions has proven challenging on routed networks such as the Internet. Routed networks operate by forwarding packets between a source and a destination through an intervening series of routers which examine the address of a packet, and use the address to forward the packet to other routers, and ultimately to the destination. Routed networks, such as the Internet, provide highly-developed addressing structures, in which millions of networked computing systems have unique addresses, and through which systems can easily communicate with each other. However, the overhead involved in routing the data from source to destination, including routing and queuing delays, makes it challenging to transmit high bandwidth traffic through a routed network with bounded latency and jitter.
In the past, routed networks carried predominately bursty traffic which was not sensitive to variations in delay. Such traffic includes e-mail and the file transfers that underlie the World Wide Web. This traffic is ideally suited to the connectionless environment provided by routers. As routed networks become more prevalent and familiar, there is an increasing demand to carry video, voice, music, and other real-time traffic. Some of this traffic is very high-speed; other of this traffic is not high speed but cannot easily tolerate variations in delay. Much of this traffic is less bursty and hence is less naturally suited to a connectionless transmission mechanism. The need to support a mix of traffic of widely varying speeds, delay tolerances, and connection longevities over a single integrated network is a difficult engineering problem.
In contrast, connection-oriented networks, such as asynchronous transfer mode (ATM) or frame relay networks, operate by establishing a connection between a source and a destination. Once the connection is established, data can be rapidly sent from source to destination using a virtual physical layer (layer one) circuit without the computing overhead and queuing delays associated with a routed network. However, connection-oriented networks do not presently have highly-developed and universal addressing structures, such as exist in routed networks such as the Internet. Although connections may be established through a connection-oriented network between a given source and a given destination, there is presently no mechanism to use non-routed connections to send IP traffic in a general or standard way. Consequently, connections cannot easily be established through connection-oriented networks between a given source and a given destination.
In order to facilitate sustained high bandwidth transmissions across routed networks, the resource reservation protocol (RSVP) has been developed. RSVP operates by reserving bandwidth along a routed network so that a high bandwidth transmission can be channeled through the routed network. As is mentioned in the Abstract of Version 1 of the RSVP protocol specification, RSVP is a resource reservation setup protocol designed for an integrated services Internet. RSVP provides receiver-initiated setup of resource reservations for multicast or unicast data flows, with good scaling and robustness properties. Thus RSVP breaks into two parts: The receiver-initiated part, and the resource reservation part. The resource-reservation part, which builds circuit-like services (supporting data flows) on a connectionless store-and-forward base, is very compute intensive for that store-and-forward base.
Another method of facilitating high bandwidth transmission is the Ipsilon Flow Management Protocol (IFMP). IFMP is a protocol which instructs an adjacent node to attach a layer two label to a specified IP flow. "The label allows more efficient access to cached routing information for that flow and it allows the flow to be switched rather than routed in certain cases. . . . If a network node's upstream and downstream links both redirect a flow at the node, then the node can switch the flow at the data link layer rather than forwarding it at the network layer." See Ipsilon Flow Management Protocol specification for IPv4 version 1.0. Hence, IFMP aims at employing the data link layer directly to carry a flow (rather than reserving router resources for the flow). However, in IFMP a centralized monitoring node or router is required to discover the flow and find a better path. The centralized node must guess the service required by the traffic and must guess the time at which the traffic is ended so that the link layer path may be reclaimed. The approach used in RSVP is superior.
What is needed is a more general, cost-effective system for providing high bandwidth transmissions or transmissions with bounded latency and jitter across computer networks.